An aerogel is a gel which has a lower density than the fully condensed form of the material comprising the gel. Aerogels typically are produced by replacing the liquid of a gel by air or another gas without allowing complete collapse of the structure. The seminal report on this was made by Kistler in 1931 (Nature, 127, 741(1931)), who described the goal of the research as being "to test the hypothesis that the liquid in a jelly can be replaced by a gas with little or no shrinkage". This early work led to aerogels through the use of supercritical fluids to extract liquid, and it led to the hypothesis that the gel structure itself can be preserved in the supercritical drying process, as disclosed by Marshall in U.S. Pat. No. 285,449 (1942).
There have been many successes in the aerogel field, as disclosed in the scientific and technical literature and in patents. Of relevance to the current invention is the area known in some contexts as Organically Modified Ceramics, referred to as ORMOCERS or called CERAMERS, which have been widely studied. A descriptive review of this area is that of R. C. Mehrotra (Present Status and Future Potential of the Sol-Gel Process, Chapter 1 in Chemistry, Spectroscopy and Applications of Sol-Gel Glasses, Structure and Bonding Series 77, Eds. R Reisfeld and C. K. Jorgensen, Springer-Verlag, Berlin, 1992). This reference points to the distinction between composite materials that are mixed at the molecular level and those that have mechanically combined components. This reference also discusses work directed to organically modified gels in the form of aerogels and their subsequently dried, fused, oxidized and otherwise treated forms. Also of relevance are works concerning aerogels and their applications. The book Aerogels edited by J. Fricke (Springer Proceeding in Physics 6, Springer-Verlag, Berlin, 1985), the book Sol-Gel Science, The Physics and Chemistry of Sol-Gel Processing by C. J. Brinker and G. W. Scherer (Academic Press, Inc. Harcourt Brace Jovanovich, Publ., New York, 1990) and the book Sol-Gel Technology for Thin Films, Fibers, Preforms, Electronics and Specialty Shapes, Ed. L. C. Klein (Noyes, Park Ridge, N.J., 1988) are of relevance and show the great importance attached to the formation of aerogels with specific properties and functions. U.S. Pat. No. 4,440,827 discloses in claim 13 the use of silica particles in media for ink jet recording and optical bar code printing, wherein one of the methods for preparing the synthetic silica that may be used is an aerogel process. The use of silica aerogel in Cerenkov detectors is described, for example , by M. Cantin, L. Koch, R. Jouan, P. Mestreau, A. Roussel, F. Bonnin, J. Moutel and S. J. Tiechner, in their paper in Nuclear Instruments and Methods, 118, 177 (1974).
Examples of aerogels which contain or have added to them, metal ions or metal containing species are well known. Those known fall into several categories, including: (1) a silica aerogel that has been dipped into a solution or dispersion containing the metal ion source; (2) a polymer matrix aerogel, such as a polyacrylonitrile aerogel, that contains metal ions added to the aerogel or to the gel before formation of the aerogel (eg. L. M. Hair, L. Owens, T. Tillotson, M. Froba, J. Wong, G, J. Thomas, and D. L. Medlin, J. Non-Crystalline Solids, 186, 168 (1995), and S. Ye, A. K. Vijh, Z-Y Wang, and L. H. Dao, Can. J. Chem. 75, 1666 (1997)); or (3) a silica aerogel having metal ions (eg. M. A. Cauqui, J. J. Calvino, G. Cifredo, L. Esquivias, and J. M. Rodriguez-Izquierdo, J. Non-Crystalline Solids, 147&148, 758 (1992)) or small metal compounds bound in it (eg. Y. Yan, A. M. Buckley and M. Greenblatt, J. Non-Crystalline Solids, 180, 180 (1995)).
The use of supported metal and metal ions for catalysis is widely known and practiced, and many reports exist in the scientific, technical, engineering, and patent literature. Relevant studies include "The Chemistry of Ruthenium in PSSA lonomer: Reactions of Ru-PSSA with CO, H.sub.2 and O.sub.2 and Alcohols" (I. W. Shim, V. D. Mattera, Jr., and W. M. Risen, Jr., Journal of Catalysis, 94, 531 (1985), which includes a report of a static Fischer-Tropsch reaction catalysis by supported ruthenium under mild conditions of 150.degree. C. and 600 Torr total pressure, "A Kinetic Study of the Catalytic Oxidation of CO over Nafion-Supported Rhodium, Ruthenium, and Platinum", by V. D. Mattera, Jr., D. M. Barnes, S. N. Chaudhuri, W. M. Risen, Jr., and R. D. Gonzalez, Journal of Physical Chemistry, 90, 4819 (1986), which shows this catalysis, and "Chemistry of Metals in Ionomers: Reactions of Rhodium-PSSA with CO, H.sub.2, and H.sub.2 O", Inorganic Chemistry, 23, 3597 (1984), which shows relationships between spectroscopic observations on supports that have been exposed to these gases and the compounds formed and the oxidation states of rhodium species.
Despite the known aerogels and metal supports, a need still remains for improved aerogels and related materials having superior properties and applicability.